Integration of remote sensing and geophysical investigation in geological mapping of the Yatta/Kwa Vonza phonolite lavas

Abstract

This research was conducted in Yatta/Kwa Vonza Ward. The ward is located in Kitui County's westernmost region, bordering Machakos and Makueni Counties to the east and south. The ward has a surface area of about 780 square kilometers. The region is part of the Neoproterozoic Mozambique Belt, and the Yatta Plateau is a major igneous intrusion. The plateau stretches from northern Machakos County to southern Kitui County, cutting through Yatta/Kwa Vonza ward and into the Tsavo. The phonolite lava is thought to have flowed along an old river bed incised in an older surface. Subsequent erosion of the adjacent gneisses resulted in the present reversed morphological feature of the Yatta Plateau. To assess the deposit's economic potential, remote sensing investigation, geological field mapping, geophysical survey and engineering tests were carried out in the area. The study used Landsat-8/OLI satellite data that was classified using ArcGIS 10.8 software. Remote sensing techniques were used to determine the geological extent of the Yatta plateau in the study area, and thus the length of the phonolites that could be mined in the Yatta/Kwa Vonza ward. From the field assessments, the phonolite deposit in the area has a thickness of 20 meters and a width of 3 kilometers, which varies along the profile due to changes in the valley channel it overlies. It covers an area of 80 square kilometers and an estimated tonnage of 4.0 billion metric tonnes. The deposits can last for 660 years with an annual production of 6 million tonnes of aggregates. Mechanical tests show that the deposit is suitable for use as an aggregate in road, rail, and bridge construction.